PITTSBURGH — The National Weather Service has issued a tornado watch for Butler County and much of Western Pennsylvania. The watch is in effect until 9 p.m. today. It also covers Adams, Allegheny, Armstrong, Beaver, Bedford, Blair, Cambria, Fayette, Franklin, Fulton, Greene, Huntingdon, Indiana, Somerset, Washington and Westmoreland counties. A watch means that weather conditions are favorable to produce funnel clouds or a tornado.